Over the last half century there have been numerous attempts to produce inexpensive semiconductor, particularly silicon, films of high quality suitable for semiconductor devices such as photovoltaics or displays. There are millions of devices which rely on some of the more successful techniques for growing semiconductor films. This, the desire to reduce cost, is an ongoing process requiring a continuous stream of small and large innovations.
Primarily cost and/or efficiency of devices made from silicon semiconductor films materials are the central issues. For example, single crystal silicon photovoltaic devices have high efficiency but are expensive compared to amorphous silicon which is relatively inexpensive to produce but devices that use it have relatively low efficiency. Single crystal silicon films can be deposited on the surfaces of single crystal silicon or sapphire. Deposition of single crystal silicon on sapphire below the melting point of glass has recently been proven, but both sapphire and single crystal silicon substrates are expensive. The ability to deposit single crystal or large grained silicon on an inexpensive substrate such as glass would therefore be very desirable. To some extent, this has also been accomplished. For example, large grained silicon films have been grown by scanning a laser beam that heats, melts, and crystallizes a silicon film deposited on glass; large grains are produced in the direction of the laser scan. However, these grains are not produced at a low enough temperature, i.e. below the melting point of glass. Large grain means the grain size is comparable to or larger than the carrier diffusion length such that electron-hole recombination at grain boundaries is negligible. In semiconductor thin films this means that the grain size is greater than or equal to the film thickness.
Here a method for producing inexpensive semiconductor, particularly silicon, films of high quality suitable for semiconductor devices such as photovoltaics or displays is disclosed. A method is also disclosed for depositing such film on an inexpensive substrate, such as glass. A method is further disclosed for depositing such film at temperatures below the melting point of glass.